Re: [Xen-devel] PCI passthrough issue

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2011-02-01 at 15:14 +0000, Jean Baptiste Favre wrote:
> Le 01/02/2011 15:18, Ian Campbell a Ãcrit :

> > Assuming the driver is modular:
> >         "modprobe sky2 copybreak=<N>"
> >
> > Depending on your distro there will be somewhere in /etc you can add
> > this. e.g. on Debian you can create a file in /etc/modprobe.d/
> > containing "option sky copybreak=<N>" other distros
> > use /etc/modprobe.conf etc.
> OK I see but it doesn't seems to have any effect.
> I tried "option sky copybreak=0" to get all packet copied with no change.

The driver is called sky2 not sky so this won't have done anything. I
typo'd it above, sorry.

> But I have to say that I'm a bit confused: as I run a PV domU, kernel
> and initrd are provided by dom0.
> So basically, I had no module related binaries installed. After
> installation, I tried to remove module and reload it with different
> configuration without changes.
> Is there any way to provide this sort of option in kernel commandline so
> that it 'll be taken into account even in initrd ?

It depends on your distro and/or initrd tool, I don't know a generic
answer. 

If the driver is statically compiled and not modular at all you can do
<module>.<param>=<value> on the kernel command line, e.g.
"sky2.copybreak=256".

There doesn't appear to be any way to find out what copybreak the driver
actually uses, short of hacking something into the driver itself. e.g.

diff --git a/drivers/net/sky2.c b/drivers/net/sky2.c
index 7d85a38..786b8c6 100644
--- a/drivers/net/sky2.c
+++ b/drivers/net/sky2.c
@@ -87,7 +87,7 @@ module_param(debug, int, 0);
 MODULE_PARM_DESC(debug, "Debug level (0=none,...,16=all)");
 
 static int copybreak __read_mostly = 128;
-module_param(copybreak, int, 0);
+module_param(copybreak, int, 0444);
 MODULE_PARM_DESC(copybreak, "Receive copy threshold");
 
 static int disable_msi = 0;

Allow you to see the current active value
in /sys/module/sky2/parameters/copybreak. If you are going to do that
you might as well just change the constant above though ;-)

Ian.


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